I enjoyed this one. I even learned a few things. :) It's a good reference for C.S. Lewis' writings.
I like that Wagner acknowledges that his readers will not all be Christians, but doesn't attempt to soften Christian themes. And he explains things that those who are not familiar with Christianity might not understand.
There's a pretty glaring error on page 13. Page 12 ends with a complete paragraph, then page 13 has a picture at the top followed by the end of a sentence... I'm surprised that wasn't fixed in editing.